Printing techniques can be broadly categorized into two groups: analog and digital. Common analog techniques are offset lithography, and flexographic, gravure and screen printing. Inkjet and electrophotographic printing are the most prevalent digital technologies. Digital printing has an advantage over its analog counterpart in that printed output can be digitally altered, meaning that every printed page can be different. To change the printed output of an analog printer, a new set of imaging plates or stencils must be produced. Digital printing methods are more cost effective at low run lengths (number of pages), whereas at large page counts analog printing may be more economical. Print quality is another vector of comparison between printing methods. Analog prints may have superior image quality and may operate at higher printing speeds than digital printing methods, where their use depends on the print job or application.
Since the mid-1980s electrophotographic (EP) printing, commonly known as laser printing, has been a popular choice among consumers who demand high quality, professional looking printed communications. State-of-the-art commercial EP printers now have image quality that rivals lithographic offset printers, although printing speed and cost may still favor analog printers for many print jobs. Dry EP or DEP employs dry toner particles. Liquid electrophotographic (LEP) printing is a variant of EP printing that has superior image quality and the advantage of being compatible with a broad substrate gamut (coated and uncoated paper, plastic sheet, cardboard, folded cartons, shrink wrap and labels, for example). LEP ink uses a dielectric carrier fluid and pigmented resin as colorant particles. Electrophoretic attraction of charged ink particles to a laser exposed photoconductor forms the image, which is transferred to a heated blanket prior to final transfer to the substrate. High quality output can be achieved at print speeds consistent with many commercial printing requirements. However, analog offset printing still may be favored for higher volume printing jobs.
Inkjet printers are now common and affordable and allow one to obtain photographic quality albeit at low printing speed. They are used in home printing, office printing and more recently, in commercial printing. Key advantages for inkjet technology in the commercial printing market are that printing width can be easily scaled and high print speeds have been achieved. Challenges facing traditional inkjet technology include a limited substrate gamut and high energy cost for removal of carrier fluid from water-based inks Carrier fluid removal can limit print speed and areal coverage.
Commercial printed media including, but not limited to, packaging cartons and boxes, envelopes, magazines, and brochures, for example, that are printed with logos, image patterns or designs, and a variety of commercial information using any of the above printing technologies, usually have an overcoat varnish to protect underlying print during shipping and handling, for example, as well as provide or enhance gloss. However, adhesive attachment to the overcoat varnish and printing on the overcoat varnish are difficult and present problems when subsequently marking or adding information to the varnish-coated printed media, such as recipient address information; or even to assembly the media as a carton from its fold-pattern. Therefore, manufacturers of the commercial printed media have to account for knock out areas in the overcoat varnish to accommodate various client specifications. Accommodation of the knock out areas for various clients is accomplished in ways that can limit the types of overcoat varnish used, and how it is applied, for example; and impact equipment durability and maintenance.
For example, in analog printing, a specific plate or mask is created to accommodate the knock outs for each client's specifications, which is suited for static data. In digital printing, overcoat varnish is applied in the areas where knock outs are not specified. For example, inkjet printing the overcoat using piezoelectric inkjet print heads may be limited to custom designed UV-curable overcoat fluids with low viscosity (and low solids content), where the piezoelectric print head tends to have considerable maintenance. In thermal inkjet printing, the thermal print heads both limit the overcoat to custom designed fluids having very low solids and viscosity and still tend to have considerable maintenance. These limitations in printing processes impact both time and cost for the commercial printed media manufacturer.
Certain examples have other features that are one of in addition to and in lieu of the features illustrated in the above-referenced figures. These and other features are detailed below with reference to the preceding drawings.